What is the difference between DA and SA/DA?

Hey,
I'm only 20 (getting ready to buy once I turn 21 in Nov.) and i'm pretty new to handguns and i've been trying to look up info online about the differences between DA and SA/DA and still can't make heads or tails of it. Heres what I've gotten out of it so far. Please correct what I have wrong:

DA - Put the magazine in, rack the slide, good to go correct?

SA/DA - Put the magazine in, rack the slide, then heres where i'm confused. after you rack it, do you have to the cock the hammer back or does it stay back, if it stays back then whats the difference between that and just DA.
i read online, which confused me more, that after the first shot then the gun is DA. so I guess i don't understand what about the gun is SA.

Hope this helps. DA or DOA (double action, double action only) models when you rack the slide and chamber a round it will remain in the DA mode. DA/SA models, when you rack the slide it will draw back the hammer and it will be in SA mode. Now depending on what gun you have if you have a decocker when the decocker is engaged it will lower the hammer to DA mode or half cocked which will still be considered DA but with a shorter pull. If not a decocker you would have to carefully decock the hammer manually to lower into DA mode or leave it "cocked and locked" and engage the safety which will have it remain in SA mode. It would help to know which handgun you have or are thinking of getting to better give advice or to answer your question.

I'm thinking of getting the Beretta PX4 storm which does come in DA/SA. So if i were to rack the gun, it would just go into SA? the thing i dont get (and maybe its because i don't fully understand DA and SA) is if it is in SA and you fire, doesn't the gun still blow back, rechamber a round and cock the hammer? if so how is that different from DA?

wow, i just looked it up on wikipedia and now i'm even more confused.
i'm sorry to be a burdon, i'm just trying to understand it all.
so i thought i knew what things mean but i guess i don't. so here it goes:

i thought a decocker completely lowered the hammer so you couldn't fire it and then to fire the gun you would have to cock the hammer and you would be able to fire. is that right?

i thought SA meant you had to cock the hammer back for each shot. is there more to that or what?

i thought DA was once you rack the slide, the gun is cocked and for every round thereafter all you had to do was point and fire. but wikipedia made SA on semi-auto guns sound exactly the same as this.

i'm very sorry for all the questions. i just want to understand before i go out and buy.

Best thing to do for your best understanding is to go to a gun shop and ask your questions. They will have handguns there to show you what the difference is between each designation. They won't laugh at you, they'll probably appreciate your trying to get the information before you purchase something you don't want. By the way, if they rent guns at that shop, try the .40 and the 9mm, then you'll know what you would like to start with.

i thought a decocker completely lowered the hammer so you couldn't fire it and then to fire the gun you would have to cock the hammer and you would be able to fire. is that right?

Yes on a SAO (single action only) pistol like the 1911, but not on a DAO or DA/SA pistol. A decocker simply decocks the weapon so it fires in double action mode. Some decockers, like on the Beretta 92FS for example, are also a safety which means the gun won't fire. But to make it fire you do not have to cock the gun, you simply take the safety off. The gun will then fire with the hammer down in double action mode.

i thought SA meant you had to cock the hammer back for each shot. is there more to that or what?

You must manually cock the gun for each shot with a single action revolver. With a SA or DA/SA semi-auto pistol, the hammer is cocked automatically after each shot by the action of the slide.

i thought DA was once you rack the slide, the gun is cocked and for every round thereafter all you had to do was point and fire. but wikipedia made SA on semi-auto guns sound exactly the same as this.

Wikipedia is more right. For either a DAO or DA/SA gun all you have to do is point and fire. On either gun when you load it you have to rack the slide to chamber a round. You are not racking the slide to cock the hammer because either will fire with the hammer down.

Here goes:

DAO (Double Action Only): The gun fires in double action mode only, meaning it is a longer, heavier trigger pull because the first part of the trigger's travel is to cock the hammer back. Only the very last part of the travel is to release the hammer. Every time the gun is fired, the slide cycles, ejecting the spent cartridge and loading a new one. On a DAO only pistol this cycle does NOT cock the hammer. Essentially the gun has an internal decocker. So, after the first shot and the slide cycles, the hammer is again down and the gun fires with the longer heavier double action pull. This continues for every shot.

DA/SA (Double Action/Single Action: The gun may be fired in double action for the first shot but then reverts to single action for the remaining shots as the slide does cock the hammer when it cycles. With the safety/decocker on, when you load the gun and rack the slide the gun will be in double action with the hammer down since the decocker was on. You simply take the safety off and now the weapon is ready to fire in double action (hammer down). All follow-up shots will be in single action because the cycling of the slide does cock the gun.

At any time, say halfway through the magazine, you can flip the decocker, and the gun will then be in double action mode for the next shot. You may fire the gun in double action, or you may cock the hammer manually and fire it in single action.

SA or SAO (Single Action Only): The gun must be cocked for the gun to fire. The trigger will not serve the function of cocking the hammer. When you load the gun and rack the slide, the gun is ready to fire with hammer back. If you manually lower the hammer, then to make the gun fire you must cock the hammer with your thumb or rack the slide in order to cock the hammer.

No problem at all and I do realize the thirst for knowledge, especially when new to firearms. However I must say that Mike's response is actually the best. Take a Basic Pistol course from an NRA certified instructor. Then you will have a hands-on understanding.

All these terms apply mostly to the trigger alone and not so much the hammer or striker.

Double Action means the TRIGGER performs the action of cocking the hammer (1) and releasing the hammer (2). You can cock the hammer in a DA revolver by hand also, then the trigger performs action (2) of releasing the hammer.

Double Action Only means the ONLY way it will fire if for the TRIGGER to cock (1) and release (2) the hammer (usually bobbed in a revolver) or the striker/bobbed hammer (in a semi-auto).

Single Action means the TRIGGER CAN ONLY release the hammer. The hammer has to be cocked either by hand (revolver) or by the slide first (semi-auto).

Double Action/Single Action (semi-auto pistols) mean the trigger will cock and release (TWO ACTIONS) the hammer, or simply release the hammer (ONE ACTION) after it has been cocked by the slide moving to the rear (either by firing or by hand).

Mahoney, you've had good and proper instruction here. However - and there's always a 'however' - the terms apply to revolvers as well as semi-automatic pistols. Also, some 'old school' semi-automatic pistols have 'de-cockers' that do lower the hammer for safety and must then be manually cocked to fire (not double action). The last one I can think of built that was the Smith & Wesson Model 52. Not a common pistol. The Polish made VIS (commonly called a Radom) is another such 'hammer dropper' pistol, but hasn't been made since WWII. One does encounter them at various places. Then there is the (very old) Colt 1903 Pocket Hammer pistol. It has a hammer and trigger much like a Government Model (1911) but has NO SAFETY and no hammer dropper. One must lower the hammer like on a single action revolver. (End of the revolver only era and was sort of a 'transition' design.) I don't think anyone makes such a handgun these days.

A decent course of 'pistol basics' - if you can find someone in your area holding such - should explain it all. Failing that, some of the old 'annuals' like Gun Digest or Shooter's Bible will have illustrations of many handguns and brief descriptions.

But whatever handgun you find, pick up or have dropped on you will have two features of serious import. The trigger and the muzzle. If you don't fiddle with the trigger, it more than likely won't fire. And if it does by some bad fortune fire, the muzzle is the end to keep away from self and loved ones.